Firebase push notification sender

FirebasePushNotificationClient.java

package sevenwinds.fool;


import lombok.Builder;
import lombok.Data;
import lombok.Singular;
import lombok.Value;
import org.springframework.http.*;
import org.springframework.web.client.RestTemplate;

import java.util.List;
import java.util.Map;

/**
 * Created by Miha on 12.12.2016.
 *
 * dep org.springframework:spring-web
 * dep org.projectlombok:lombok
 */
@Data
public class FirebasePushNotificationSender {

    String url = "https://fcm.googleapis.com/fcm/send";
    String serverApiKey;

    private final RestTemplate restTemplate;
    private final HttpHeaders headers;

    public FirebasePushNotificationSender() {
        restTemplate = new RestTemplate();
        headers = new HttpHeaders();
        headers.setContentType(MediaType.APPLICATION_JSON);
        headers.set("answer", "json");
    }

    public void setServerApiKey(String serverApiKey) {
        this.serverApiKey = serverApiKey;
        headers.set("Authorization", "key=" + serverApiKey);
    }

    public PushResponse send(PushMessage message) {
        HttpEntity<PushMessage> entity = new HttpEntity<>(message, headers);
        ResponseEntity<PushResponse> exchange = restTemplate.exchange(url, HttpMethod.POST, entity, PushResponse.class);
        return exchange.getBody();
    }

    public static void main(String[] args) {
        FirebasePushNotificationClient androidPush = new FirebasePushNotificationClient();
        androidPush.setServerApiKey("AAAAs7MNMC***");
        PushMessage message = PushMessage.builder()
                .to("cWD8Y***")
                .priority(Priority.normal)
                .dataItem("message", "hello")
                .dataItem("sender", "friend")
                .notification(NotificationParam.builder().body("Hello").title("New message").build())
                .build();
        PushResponse send = androidPush.send(message);
        System.out.println(send);
    }

    /**
     * @see <a href="https://firebase.google.com/docs/cloud-messaging/http-server-ref#downstream-http-messages-json">Firebase doc 1</a>
     * @see <a href="https://firebase.google.com/docs/cloud-messaging/concept-options">Firebase doc 2</a>
     * */
    @Builder
    @Value
    public static class PushMessage {
        String to;
        Priority priority;
        Integer time_to_live;
        String collapse_key;
        Boolean content_available;
        @Singular("dataItem") Map<String, Object> data;
        NotificationParam notification;
    }

    @Data
    public static class PushResponse {
        long multicast_id;
        int success;
        int failure;
        int canonical_ids;
        List<ResponseResults> results;
    }

    @Data
    public static class ResponseResults {
        String error;
        String message_id;
    }

    @Builder
    @Value
    public static class NotificationParam {
        //<common>
        String title;
        String body;
        String sound;
        String click_action;
        String body_loc_key;
        String body_loc_args;
        String title_loc_key;
        String title_loc_args;
        //</common>

        //<ios>
        String badge;
        //</ios>

        //<adnroid>
        String icon;
        String tag;
        String color;
        //</android>


    }

    public enum Priority {
        normal,
        high,
    }
}